ui: keep a gap before the first library tab

Put an 8dp spacer at the start of the scrollable content and let the
reveal leave that gap when scrolling back towards the first tab, so the
selected pill no longer sits flush against the screen edge. The spacer
scrolls away, so a tab that is half off is still cut at the edge.

app/src/test/kotlin/com/subtracks/ui/LibraryScreenTest.kt

@@ -464,6 +464,41 @@ class LibraryScreenTest {
         assertTabFullyVisible(LibraryTab.Playlists, labelWidth)
     }
 
+    @Test
+    @Config(qualifiers = "de-rDE-w320dp-h640dp-xhdpi")
+    fun returningToTheFirstTabLeavesAGapAtTheEdge() {
+        val selectedTab = mutableStateOf(LibraryTab.Playlists)
+        composeRule.setContent {
+            SubtracksTheme {
+                LibraryScreen(
+                    selectedTab = selectedTab.value,
+                    onTabSelected = { selectedTab.value = it },
+                    albums = remember { flowOf(PagingData.empty<Album>()) },
+                    artists = remember { flowOf(PagingData.empty<Artist>()) },
+                    playlists = remember { flowOf(PagingData.empty<Playlist>()) },
+                    coverArt = { _, _ -> null },
+                    onAlbumClick = {},
+                    onArtistClick = {},
+                    onPlaylistClick = {},
+                    onSync = {},
+                    onOpenSettings = {},
+                )
+            }
+        }
+        composeRule.waitForIdle()
+
+        composeRule.runOnIdle { selectedTab.value = LibraryTab.Home }
+        val expectedGap = with(composeRule.density) { TAB_EDGE_GAP.toPx() }
+        composeRule.waitUntil(5_000) { tabBounds(LibraryTab.Home).left <= expectedGap + 1f }
+
+        assertEquals(
+            "the first tab should keep a gap from the screen edge",
+            expectedGap,
+            tabBounds(LibraryTab.Home).left,
+            1f,
+        )
+    }
+
     private fun assertTabFullyVisible(
         tab: LibraryTab,
         labelWidth: Float,
@@ -549,3 +584,4 @@ class LibraryScreenTest {
 }
 
 private val TAB_LABEL_CHROME = 56.dp
+private val TAB_EDGE_GAP = 8.dp